The present invention relates to a novel method of high frequency pulse arc welding and an apparatus therefor.
It is known that, in a conventional high frequency pulse arc welding method, as the peak value of the high frequency pulse current is increased, a quenching force produced by electromagnetic force becomes larger, and, consequently, the stiffness of the arc and the pressure of the arc are increased. It is also believed that the vibration effect of the high frequency peak pulse current can decrease the grain size of a welding portion and reduce blowholes. However, the welding current used in actual welding includes a ripple current due to the inductance L of the welding cable, as shown in a typical apparatus in FIG. 12, and, accordingly, there is a disadvantage in that the effect of the high frequency pulse current cannot be obtained sufficiently.
Further, in a conventional direct current TIG arc welding method, a stiffness of the arc is obtained by a gas pinching force, using a mixed gas of argon and hydrogen for the shielding gas, as a means for giving the arc stiffness (directivity). This stiff arc is used for welding with a very narrow edge groove on austenitic stainless steels. However, this welding method cannot be used for the welding of ferritic stainless steels or certain other steels because of hydrogen embrittlement. Further, this welding method cannot be used for the welding of aluminum or aluminum base alloys because hydrogen tends to cause the formation of a blowhole. On the other hand, the conventional pulse welding cannot be applied to aluminum welding either because of the lack of cleaning action.
Arc welding methods and apparatuses based on the use of a high frequency pulse current are disclosed in Japanese Patent Application Laid-Open No. 53-119758, Japanese Patent Application Laid-Open No. 54-131548, and Japanese Patent Application Laid-Open No. 59-92169.
In the past, the pulse arc welding method has produced a small arc stiffness, and, consequently, it has been difficult to perform welding with a narrow weld edge groove and welding with a deep melting penetration.